Organic second-order nonlinear optical (NLO) polymers have received increasing interests due to their potential for applications in high-speed electro-optic (E-O) devices with very broad bandwidth and low drive voltage, and that can be made with cost effective fabrication process. In order to be qualified for practical devices, a material needs to possess simultaneously large and thermally stable E-O activity, and good processibility. Although some of the above-mentioned requirements have been satisfied individually, the success of integrating all these desirable properties in a single material system has not yet been realized and remains a very challenging task. For example, large E-O coefficients have been demonstrated in several guest/host poled polymers, but these materials often suffer from low poling-induced alignment stability and poor solvent resistance during the multi-layer fabrication process. Thus, it is desirable to be able to covalently incorporate chromophores into a polymer network and harden the matrix through crosslinking reactions to improve both thermal and mechanical properties. However, a reduction of 20-40% in E-O activity is usually accompanied with this approach. E-O activity is reduced because typical poling of conventional NLO thermoset polymers is achieved through a sequential lattice hardening and poling process. As a result, the lattice hardening significantly reduces the chromophore orientational flexibility due to the increase of glass-transition temperature (Tg) and interchain entanglements of the polymers, which severely inhibit chromophore reorientation under the poling field, resulting in a decreased poling efficiency. In addition, high temperatures needed for curing these polymers often cause decomposition of highly polarizable chromophores.
To overcome this nonlinearity-stability problem, the lattice hardening process should be ideally separated from the poling process that requires high rotation freedom of chromophores. In addition, because most of the highly efficient NLO chromophores possess only moderate chemical and thermal stability, very mild conditions should be employed for lattice hardening.
Accordingly, a need exists for a method for making an NLO polymer that allows for high rotation freedom of NLO chromophores during the poling process and relatively mild conditions for lattice hardening. The present invention seeks to fulfill this need and provides further related advantages.